1. Field of the Invention
This invention relates to invasive medical devices. More particularly, this invention relates to ablation of tissue using such devices.
2. Description of the Related Art
Ablation of body tissue using electrical energy is known in the art. The ablation is typically performed by applying alternating currents, for example radiofrequency energy, to the electrodes, at a sufficient power to destroy target tissue. Typically, the electrodes are mounted on the distal tip of a catheter, which is inserted into a subject. The distal tip may be tracked in a number of different ways known in the art, for example by measuring magnetic fields generated at the distal tip by coils external to the subject.
A known difficulty in the use of radiofrequency energy for cardiac tissue ablation is controlling local heating of tissue.
Self-regulating tissue ablators have been proposed to achieve the desired control. For example, PCT International Publication WO 9600036 discusses ablation of body tissue in which ablating energy is conveyed individually to multiple emitters in a sequence of power pulses. The temperature of each emitter is periodically sensed and compared to a desired temperature established for all emitters to generate a signal individually for each emitter based upon the comparison. The power pulse to each emitter is individually varied, based upon the signal for that emitter to maintain the temperatures of all emitters essentially at the desired temperature during tissue ablation.
U.S. Patent Application Publication No. 2008/0300588 proposes performing ablation automatically by monitoring system parameters. When the ablation is complete, as determined by a processor based on its reading of the system parameters, RF energy delivery is halted. The determination is made, preferably without the need for user interaction, based upon the system parameters and a set of rules for determining completion. Parameters that may be monitored include power output.